When Zappos released its API, there was a strange restriction: no mobile applications. While sometimes lawyers write terms that aren't formally enforced, Zappos made it clear on its API mailing list that it was serious. Soon, the restriction will be removed and mobile applications will be allowed without written approval.

Popular room rental service AirBNB does not yet have an official AirBNB API. But signs point to one's existence, as well as an affiliate plan in place to pay developers for reservations booked through the API. If the company sticks with the plan as written now, developers will be able to make up to 10 million API calls per day before contacting AirBNB.